Member of the House of Keys, and one of the two commissioners the Keys sent to Britain over the sale of the Island.

In March 1765 the Keys resolved that Thomas Moore and Hugh Cosnahan, gentlemen and members of their House, should be their commissioners in the name and on behalf of the people of the Isle, to take such steps as they were advised to support and maintain the constitution, rights and privileges of the Island by application to the ministry or parliament of Great Britain, and to obtain such terms as were consistent with the welfare of the Isle. The two of them presented a petition to the House of Commons on behalf of themselves and the rest of the Keys as representatives of the people.

His evidence to the 1792 inquiry is the reason the delegation matters to the record. Examined at Douglas on 27 September 1791, and cross-examined by the Duke of Atholl, he said that January 1765 was the first time any rumour of the treaty for the sale reached the Island. The commissioners used the Keys' petition to prove two things: the delegation itself, and that no meeting of the Keys was called by the Governor until 19 March, nearly a month after the transaction of the sale was closed. In another examination the moment is dated more precisely still, when Hammersley asked Quayle whether he had let the inhabitants know of the treaty and Quayle said that he had, at which Cosnahan and others present declared that they had received no notice of it and must have heard had any been given.

He was still writing on Island business two decades later, in letters to George Farquhar from Douglas in May 1789 and April 1790.